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Show 1906.] IN MEXICAN LIZARDS. 339 be called C. gularis mexicanus, in opposition to C. gularis communis, but not possibly could it be named .1 race of communis. Lastly, on Cozumel Island, off Yucatan, C. communis reappears, so that we ma}' infer its occurrence in Yucatan. CNEMIDOPHORUS COMMUNIS OCCIDENTALIS. (Text-figs. 69, 77 A-F, 78 B, 79 A.) Diagnosis.-4 supraoculars. Strong collar. Posterior side of forearm with scutes or enlarged polygones. Stripes broken up, in the adult, into rows of round spots; fields with similar rows of spots. Humeral rows of scales 5-7. Femoral rows 6-7, mostly 6. Pores 16-21. Length rarely exceeding 100 m m. Range the same as that of the Sierra Madre occidental, from N.W. Chihuahua to Jalisco. Specimens from Ixtlan differ considerably in their colour-pattern, approaching thereby C. mexicanus of Oaxaca-a very significant case of convergence. On the Central plateau C. communis seems to remain somewhat smaller, with less emphasised characters in coloration ; but it reappears intensified at Puebla. Such an extension across the country, from Jalisco, across Guadalajara towards and beyond Guanajuato and Qneretaro, conforms well with the physical features of the country ; and in m y paper on " The Distribution of Mexican Amphibians and Reptiles," Proc. Zool. Soc. 1905 (vol. ii. p. 191), I have been able to show the existence of such an exchange. Whether these Cnemidophori ascended through this Jalisco gap, or descended thither from the plateau and from the bases of the Western Sierra Madre, is another question. Lake Santa Maria (text-fig. 78 B ) in N . W . Chihuahua.-The single specimen is remarkable for having only 3 supraoculars on the left side, whilst the 4th right is very small. The collar consists of only one row of scales, which are rather small, and nearly all of the same size. The posterior surface of the forearm shows three rows of large polygones, none of which can be called large scutes. The other structural features likewise afford no decided clue to the affinity of this specimen. Throat and collar are white, with a bluish tinge across the mid-throat and across the collar excepting the row of larger scales. Chest and abdomen white, with bluish bases to some of the scales. Tail, hind and fore limbs, and anal region are white beneath. The upper surface is uniformly slaty grey, rather dark, with many small whitish specks, especially on the lower back, rump, thighs, and root of tail. Of the original stripes, only faint traces of stripes 1 and 2 are still visible. The dusky band across the collar and the small whitish and bluish dorsal spots undoubtedly point to the relationship of this specimen with those of Tuxpan (text-fig. 79 A ). Durango, from the foot of the Iron Mountain, on rather barren ground (text-fig. 77 C).-Supraoculars 4. Collar composed of large scales, mostly with an imperfect, once with a complete row PROC. ZOOL. Soc-1906, VOL. I. No. XXIII. 23 |